1. Field of the Invention
The present invention relates to a focus detection sensor to be used for automatic focus detection and an optical apparatus using the focus detection sensor.
2. Description of the Related Art
There is conventionally known, for example, an image capture apparatus having an auto focus (to be referred to as AF hereinafter) function of adjusting the in-focus distance of an imaging lens in accordance with the focus detection state of a subject detected by a focus detection sensor, including a photoelectric conversion device, and automatically focusing on the subject. Also known is controlling the charge accumulation time or the output gain of the photoelectric conversion device of the focus detection sensor based on the brightness or contrast of a subject.
For example, in Japanese Patent Laid-Open No. 2006-251777, a focus detection sensor uses line sensors each comprised of a plurality of photoelectric conversion devices (pixels). Each line sensor is divided into a plurality of areas, and accumulation is stopped in each area when the difference (contrast) between the maximum value and the minimum value of pixel signals has exceeded a target value.
In addition, Japanese Patent Laid-Open No. 10-333021 discloses arranging a monitor sensor near a line sensor pair used for focus detection and controlling the accumulation (integration) time of the line sensor pair based on the signal from the monitor sensor.
In the arrangement disclosed in Japanese Patent Laid-Open No. 2006-251777, however, since charges photoelectrically converted by the pixels are always transferred to the accumulation circuit, noise generated in the accumulation circuit during accumulation is also accumulated, like the photoelectrically converted charges. When the accumulation time is long, the amount of generated noise also increases. For this reason, the influence of noise components in the accumulation result is not negligible, and may lead to an error in the focus detection result.
On the other hand, in the arrangement disclosed in Japanese Patent Laid-Open No. 10-333021, since accumulation control is done based on the output of the monitor sensor provided separately from the line sensors, charges photoelectrically converted by the pixels need not be transferred to a memory circuit or a monitor circuit. Hence, generated noise can be reduced by resetting the memory circuit or the monitor circuit until the end of accumulation in the pixels.
In the arrangement of Japanese Patent Laid-Open No. 10-333021, however, it is necessary to arrange the monitor sensor near the line sensors. In addition, the monitor sensor needs to perform accurate photometry to appropriately control the accumulation. When a plurality of line sensors are arranged, the monitor sensor restricts the layout of the line sensors. To accurately perform photometry, the arrangement of the monitor sensor itself is also restricted. As a result, the chip area of the focus detection sensor may become larger to increase the cost or impede downsizing of an optical apparatus using the focus detection sensor.